The optical communication systems have been evolving rapidly in recent years in order to adapt to the continuously increasing demand on transmission capacity, coming mainly from the growing popularity of the Internet and multimedia in everyday life. In order to keep the system complexity reasonably low, the new optical communications solutions have to offer affordable upgrades of currently available optical communication systems operating at lower speeds to satisfy the required higher speeds. One such approach was based on multidimensional coded modulation. Namely, by increasing the number of dimensions (i.e., the number of orthonormal basis functions), we can increase the aggregate data rate of the system without degrading the bit error rate (BER) performance as long as orthogonality among basis functions is preserved. Most of the papers on multidimensional signal constellations for optical communications so far have been related to single carrier systems.
In the recent years, with the rapid growth of data-centric services and the general deployment of broadband access networks, there have been strong demand driving the DWDM network upgrade from 10 Gb/s per channel to more spectrally-efficient 40 Gb/s or 100 Gb/s per channel, and beyond. The 100 Gb/s Ethernet (100 GbE) is currently under standardization for both local area networks (LANs) and wide area networks (WANs). The next natural step would be the introduction of 1 Tb/s Ethernet (1 TbE).